[ fee-aht, -at; fahy-uh t, -at ]
/ ˈfi ɑt, -æt; ˈfaɪ ət, -æt /


an authoritative decree, sanction, or order: a royal fiat.
a fixed form of words containing the word fiat, by which a person in authority gives sanction, or authorization.
an arbitrary decree or pronouncement, especially by a person or group of persons having absolute authority to enforce it: The king ruled by fiat.

Nearby words

  1. fiancé,
  2. fiancée,
  3. fianna,
  4. fianna fáil,
  5. fiasco,
  6. fiat justitia, ruat caelum,
  7. fiat lux,
  8. fiat money,
  9. fib,
  10. fiber

Origin of fiat

1625–35; < Latin: let it be done, 3rd singular present subjunctive of fierī to become

fiat justitia, ruat caelum

[ fee-aht yoo s-tee-tee-ah roo-aht kahy-loo m; English fee-aht juhs-tish-ee-uh roo-at see-luh m, fahy-uh t ]
/ ˈfi ɑt yʊsˈti tiˌɑ ˈru ɑt ˈkaɪ lʊm; English ˈfi ɑt dʒʌsˈtɪʃ i ə ˈru æt ˈsi ləm, ˈfaɪ ət /


let there be justice though the heavens fall.

fiat lux

[ fee-aht loo ks; English fee-aht luhks, fahy-uh t ]
/ ˈfi ɑt ˈlʊks; English ˈfi ɑt ˈlʌks, ˈfaɪ ət /


let there be light. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for fiat

British Dictionary definitions for fiat


/ (ˈfaɪət, -æt) /


official sanction; authoritative permission
an arbitrary order or decree
mainly literary any command, decision, or act of will that brings something about

Word Origin for fiat

C17: from Latin, literally: let it be done, from fierī to become

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for fiat



"authoritative sanction," 1630s, from Latin fiat "let it be done" (also used in the opening of Medieval Latin proclamations and commands), third person singular present subjunctive of fieri, used as passive of facere "to make, do" (see factitious). Also sometimes a reference to fiat lux "let there be light" in the Book of Genesis.

Online Etymology Dictionary, © 2010 Douglas Harper